The popularity of metal and metal oxide coated glasses in architectural and automotive design is well known. As reported prolifically in patent and other literature, such glasses, usually achieve, through the manipulation of the coating's layering system, quite acceptable degrees of reflectance, transmittance, emissivity, chemical resistance, and durability, as well as the color desired. See, for example, in this respect, U.S. Pat. Nos. 3,935,351; 4,413,877; 4,462,883; 3,826,728; 3,681,042; 3,798,146; and 4,594,137 just to name a few.
It has also been well reported that while several reasonably acceptable techniques exist for applying such coatings, one of the most efficacious, and thus preferred, is the well known technique referred to as "magnetically enhanced sputter coating". Such a technique is reported in U.S. Pat. No. 4,166,018, a recognized fundamental teaching on the subject. (See also, Munz et al "Performance and Sputtering Criteria of Modern Architectural Glass Coatings", SPIE Vol. 325, Optical Thin Films, 1982, pp. 65-73.)
While efficacious for many known layer systems, the use of certain older sputter coating system has been known to result in mechanical durability qualities less than that achieved by another known method called the "pyrolytic" technique. As a reverse function, however, sputter-coated systems often achieve better infrared reflectance than typical pyrolytic coatings. Also, sputter-coated glasses have generally been recognized as having superior optical and thermal performance characteristics than pyrolytically formed coatings, such as having improved coating uniformity, good emittance, and better solar performance characteristics. It is clear, that if a sputter-coating technique could be devised for a particular coating system wherein the mechanical durability qualities of the sputter-coated system could approach or equal that of a pyrolytic technique, while at the same time achieving the enhanced benefits of sputter-coated technology, a significant step forward in the art would be made.
In U.S. Pat. No. 5,229,194, entitled "Improved Heat Treatable Sputter-Coated Glass Systems" there are disclosed certain unique layer systems that achieved this significant step forward in the art. These systems are prior art to the subject invention due to commercial sale more than one year prior to our filing date herein. They are discussed more fully below.
Firstly, however, it should be stated that in recent years, the popularity of coated glasses has occasioned numerous attempts at achieving a coated glass article which, prior to heat treatment, can be coated, and which thereafter, can be heat treated without adversely changing the characteristics of the coating or the glass itself (i.e. the resulting glass article). One of the reasons for this is, for example, that it can be extremely difficult to achieve a uniform coating on an already bent piece of glass. It is well known that if a flat glass surface can be coated and thereafter bent, much simpler techniques can be used to get a uniform coating than if the glass has been previously bent. This is true, in this respect, for architectural and residential glass, but is particularly true for automotive glass such a bent glass windshields which in recent years have had to take on more aerodynamically efficient designs to aid in achieving increased fuel economy.
Certain techniques have been developed in the past for making coated heat treatable glass articles which may then, and thereafter, be heat treated by way of tempering, bending, or a technique known as "heat strengthening". Generally speaking, many of these prior coated articles have suffered from not being heat treatable at the higher, elevated temperatures necessary to achieve economic bending, tempering, and/or heat strengthening (i.e. 1150.degree. F.-1450.degree. F.). In short, such techniques have often suffered from a need to keep the temperature at approximately 1100.degree. F. or less in order to achieve heat treatability without adversely affecting the coating or its substrate.
This latter situation; namely the absence of any substantial adverse affect upon the coating or its substrate, defines what is meant herein by the term "heat treatable". While in certain situations, some characteristics may change somewhat during heat treatment, to be "heat treatable" as used herein means that the desired properties of the ultimate layer system and overall product must be achieved despite the fact that the coated glass has been subjected to one or more of the heat treatments discussed above (i.e. bending, tempering and/or heat strengthening). For most architectural purposes contemplated by this invention optimized heat treatability means that the glass and its layered coating remains substantially unchanged in its visual (optical) appearance as between the pre-heat treated product and the final product after heat treatment. For most automotive purposes change for the better due to the heat treatment may be tolerated and is even desirable, so long as optimized heat treatability means that the change takes place uniformly across the substrate and is independent of the parameters used to perform the heat treatment.
In this respect, U.S. Pat. No. 5,188,887 discloses certain prior art coating systems which are heat treatable because they can be heat treated successfully at the higher, more elevated temperatures aforesaid, to achieve the desired result despite having gone through tempering, bending or heat strengthening. Generally speaking, these prior art coating compositions find their uniqueness in a layering system which employs as a metallic layer, a high nickel content alloy which, in its preferred form, is an alloy known as Haynes 214, consisting essentially of 75.45% Ni, 4.00% Fe, 16.00% cr., 0.04% C, 4.50% Al, and 0.01% Y (percentages are by weight). By using a high nickel content alloy, such as Haynes 214, and overcoating it with stoichiometric tin oxide (SnO.sub.2) either alone or with other layers (such as an undercoat of the same stoichiometric tin oxide and/or an intermediate layer of aluminum between the top SnO.sub.2 layer and the high content nickel alloy), it was found that heat treatability of glass articles at elevated temperatures of from approximately 1150.degree. F.-1450.degree. F. from about 2-30 minutes, could be achieved without substantial degradation of color, mechanical durability, emissivity, reflectance or transmittance. These compositions therefore constituted a significant improvement over prior heat treatable systems such as those disclosed in the following U.S. Pat. Nos. 4,790,922; 4,816,034; 4,826,525; 4,715,879; and 4,857,094.
In addition to the above disclosures in the aforesaid patents, the Leybold windshield glass system TCC-2000 is also known. In this system, four or five layers of metals and metal oxides are employed to obtain a sputter-coated glass which, being somewhat heat treatable at temperatures up to 1100.degree. F. may be used as a pre-coated glass for making bent or unbent, glass windshields, provided that rapid time limits are placed on the heat treatment. The layering from glass substrate outwardly usually includes a first layer of tin oxide, a second layer of nickel/chrome alloy (usually about 80/20), a third layer of silver, a fourth layer of the nickel/chrome alloy, and a fifth layer of tin oxide. In addition to the rather low upper limit on heat treatment temperature and times, the resultant coatings are rather soft and exhibit such unacceptably low chemical resistance characteristics that they can realistically be used only on the inner surfaces of laminated glass windshields.
In the aforesaid U.S. Pat. No. 4,715,879 it is specifically taught that the layering system therein cannot be achieved unless the protective layer of a metal oxide (e.g. tin oxide) be formed such that the oxide has an oxygen deficit (i.e. is non-stoichiometric). This, of course, requires delicate balancing in the manufacturing process. Heat treatability, in this respect, is also disclosed in U.S. Pat. No. 4,826,525. However, in this patent it is specifically taught that a layer of aluminum must be applied to achieve heat treatability.
In the aforesaid U.S. Pat. No. 5,229,194, a significant advance in heat treatable sputter coatings is disclosed, even when compared to those disclosed in U.S. Pat. No. 5,188,887. In that invention it was found that unique results in the area of heat treatable sputter-coated glasses were achievable, particularly when used as "privacy" windows in vehicles, if metallic nickel or a high content metallic nickel alloy layer were surrounded by an undercoat and overcoat of a separate layer of an oxide or nitride of nickel or high content nickel alloy, and a further overcoat of an oxide such as SnO.sub.2, ZnO, TiO.sub.2 or oxide alloys thereof was employed. Silicon is also mentioned as useful for the first overcoat of the metallic nickel-containing layer.
Such layering systems in their preferred forms proved particularly heat treatable and abrasion resistant. However, while some were found initially to be chemically resistant, certain systems when put into mass production were found not to pass the rather rigorous 5% HCl boil chemical resistance test (discussed below). Their infrared and UV reflectance characteristics were, however, found to be excellent for a wide range of uses. Still further, however, their visible light transmittance values, desirably low for "privacy" window use, nevertheless proved to be too low to be truly useful as glass windows or panels for architectural or residential purposes where high visible light transmittance is required. Thus when production called for the sputter-coater to fulfill orders for architectural or residential coated glass after glass sheets for "privacy" windows had been coated, the coater had to be shut down so that a new layer system could be formed. If such a shutdown could be avoided a significant economic advance would be accomplished.
In commonly owned U.S. Pat. No. 5,344,718, there are disclosed certain unique sputter-coated layering systems having unique applicability for architectural and residential purposes because of their achievement of not only good chemical and mechanical durability, but their solar management properties as well. These systems are properly deemed "low-E" glasses (coatings) because their hemispherical emissivity (E.sub.h) was generally less than about 0.16 and their normal emissivity (E.sub.n) was generally less than about 0.12. Measured another way their sheet resistance was preferably less than about 10.50 ohms/square. In addition, for normal glass thicknesses (e.g. 2 mm-6 mm) visible light transmittance was preferably about 78% or more (compared to less than about 22-23% in certain preferred embodiments of the aforesaid heat treatable "privacy" window layer systems).
The invention in the aforesaid U.S. Pat. No. 5,344,718 achieved its unique low-E, high visible light transmittance values, along with its good chemical durability and resistance to abrasion, by employing a layer system which generally comprised (from glass outwardly) an undercoat layer of Si.sub.3 N.sub.4, a first layer of nickel or nickel alloy, a layer of silver, a second layer of nickel or nickel alloy, and an overcoat layer of Si.sub.3 N.sub.4. In certain preferred embodiments, the layer system from glass outwardly consisted essentially of: EQU Si.sub.3 N.sub.4 /Ni:Cr/Ag/Ni:Cr/Ag/Ni:Cr/Si.sub.3 N.sub.4
This seven layer system was found to exhibit somewhat higher durability and scratch resistance characteristics than the above-described five layer system. In each system, however, the preferred Ni:Cr layer was nichrome, i.e. 80/20 by weight Ni/Cr, and in which a substantial portion of the chromium formed as a nitride of Cr because the Ni:Cr layer was formed in a nitrogen-containing atmosphere.
Unfortunately, these durable, low-E, high visible transmittance glass layer systems proved to be non-heat treatable. This has now been found to be true not because of any oxidation of the silver layer(s) but because the metallic silver layer(s) during heat treatment become(s) discontinuous due to non-wetting; in this case because the Ni:Cr surrounding layers are insufficient to maintain the continuity of the silver layer(s) during heat treatment. Thus these otherwise advantageous layer systems could not be used where the layered glass was thereafter to be heat treated as by tempering, heat strengthening and bending. Unfortunately the silver layers were necessary to employ in order to achieve the desired low-E levels.
It is to be remembered in this respect that it is not just in the automotive windshield art where heat treatable sputter-coated layer systems find their utility. Certain architectural and residential uses also require the coated glass to be tempered, bent, or heat strengthened. Still further, the low-E glass systems of the aforesaid invention in U.S. Pat. No. 5,344,718 could generally not be adjusted to achieve low enough visible transmittance values to make them useful in "privacy" windows, even if they were heat treatable . . . which they were not. For these reasons then, these low-E glass systems did not overcome the aforesaid production problem of having to shut down the system to satisfy the needs of customers requiring widely varying solar management characteristics in their sputter-coated glass products.
Compounding the above-described problem was the problem created in the sputter-coating chamber by the need to create an Si.sub.3 N.sub.4 layer or layers in the layering system of the aforesaid U.S. Pat. No. 5,344,718. In order to achieve such a layer, an Si target (usually doped with aluminum) as the cathode was employed. Sputter coating was then conducted in an N.sub.2 containing atmosphere to create Si.sub.3 N.sub.4 by reaction. Unfortunately Si.sub.3 N.sub.4 is a non-conductor (as is the small amount of aluminum nitride formed from the Al dopant which also coats the anode during sputter-coating). Coating efficiency deteriorates and shutdown times can be extensive.
In commonly owned U.S. Pat. No. 5,403,458, a unique solution to this problem is disclosed. Generally speaking, the solution is to create a cathode target which has a prescribed amount of a conductive metal dispersed in the Si so that its nitride (or the metal if it does not form a nitride during the sputter-coating operation) forms on the anode in sufficient amounts to maintain conductivity for an enhanced period of time, thus avoiding numerous shutdowns. The entire disclosure of this copending application is incorporated herein by reference.
Heretofore if the skilled artisan wished to continue to achieve the known benefits of abrasion and corrosion resistance by using Si.sub.3 N.sub.4 layers, but also wished to avoid costly downtime, while at the same time needing to achieve heat treatability and yet have flexibility to vary the solar management properties over a reasonably wide range to avoid further production shutdowns (to meet the needs of different customers), that artisan was faced with an unsolvable problem. In this respect, the mere choice of any conductive metal as the dispersant (i.e. dopant) in an Si target would not inherently solve the problem, for that metal, while overcoming the anode coating problem may well defeat heat treatability and/or the desired levels of durability, and/or solar management (including color) characteristics which must be achieved.
It is therefore, apparent that there exists a need in the art for a sputter-coated layer system which achieves the benefits of sputter-coating while overcoming the above-described problems and drawbacks in the art. It is a purpose of this invention to fulfill this need in the art as well as other needs which will become apparent to the skilled artisan once given the following disclosure.